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I. " On the Effect of Pressure on Electric Conductibility in 

 Metallic Wires." In a Letter from M. ELIE WARTMANN 

 of Geneva, to Major-General SABINE, Treas. and V.P.R.S. 

 Communicated by Prof. W. H. MILLER, For. Sec. R.S. 

 Received January 12, 1859. 



Geneva, January 3rd, 1859. 



My dear Sir, The newspapers having reported that a society of 

 English shareholders intends to lay a second cable for transatlantic 

 telegraphy, you will allow me to give here a brief account of some 

 experiments by which I have succeeded in proving the effect of 

 pressure on electric conductibility in metallic wires. 



The method which I have resorted to i& the one devised by 

 MM. Christie and Wheatstone, which is called the electrical bridge. 

 The current of a Bunsen's battery of six large cells was divided 

 between the wire to be tested (a very soft copper wire 0'05 of an 

 inch in diameter, and covered with gutta percha) and another con- 

 ductor ; both being connected with a delicate Ruhmkorff's galvano- 

 meter, so that the needle remained on the zero point. All contacts 

 were made invariable by solderings. 



No sensible effect being determined by the pressure of nine atmo- 

 spheres in a piezometer, I made use of a press which enabled me to 

 produce compressions superior to four hundred atmospheres, conse- 

 quently superior to that which is suffered by an electric conductor 

 immersed in the ocean, at a depth of 12,420 English feet. The 

 wire, besides its coating, was preserved against permanent defor- 

 mation by two sheets of thick gutta percha, placed between the 

 steel plates which took hold of it. 



The experiments have shown 



1. That a pressure of thirty atmospheres (a number relative to 

 the sensibility of the galvanometer) diminishes the conducting power 

 of a copper wire for electricity. 



2. That the effect increases with the pressure. 



3. That the diminution remains the same for each compression, 

 as long as the latter does not vary. 



4. That the primitive conducting power is exactly restored when 

 the pressure vanishes altogether. 



Many interesting results flow from these conclusions, which I pro- 



